1. Field of the Invention
The present invention relates to a method of manufacturing a bead inductor for use in a noise controlling device or other electronic device.
2. Description of the Related Art
As a noise controlling device, especially a device for use with a microprocessor, for example, which is required to pass a large electric current therethrough, an experimental bead inductor has been proposed and tested. Such a bead inductor is an example of an experimental device which has not been publicly disclosed and is formed of a resin material or a rubber material including a powdery magnetic substance such as ferrite powder having a conductor coil embedded therein. In such a bead inductor, a conductor coil is embedded into a resin material or a rubber material via injection molding or other process, to form a molded body which is cut off at both ends thereof to expose both ends of the coil disposed therein. Then, metal caps are connected thereto via conductive resin paste or spot welding so as to define external terminals.
FIGS. 12 and 13 are sectional views illustrating a method for manufacturing a conventional bead inductor. Referring to FIG. 12, a metallic mold for injection molding to manufacture the bead inductor includes an upper mold 1 and a lower mold 2. A cavity 3 is formed in the upper mold 1 and defines a space for molding a resin. In the lower mold 2, a pin 4 is provided so as to be disposed in the cavity 3 when the upper mold 1 and the lower mold 2 are mated with each other. The upper mold 1 has a gate 1a for supplying a molten resin into the cavity 3.
In order to manufacture the conventional bead inductor using the metallic mold shown in FIG. 12, the pin 4 is inserted into a coreless coil defining an internal conductor. Then, the molten resin including a powdered magnetic substance such as ferrite powder is injected into the cavity 3 from the gate 1a. Thereby, the outer portion of the coil inserted by the pin 4 therein is molded.
FIG. 13 is a sectional view showing an outer resin portion 8a of the coil 5 molded in this manner. Then, the pin 4 is removed and the same resin as the outer portion of the coil 5 is injected into the space formed when the pin is removed, to mold the inner portion of the coil 5.
Both end portions of the molded body obtained in this manner are cut off by a dicing saw or other cutting device, such that both end portions of the coil are exposed. Metallic caps are attached to both end portions of the molded body so as to electrically connected to the exposed both end portions of the coil by conductive resin paste, spot welding, or the like.
FIGS. 14 and 15 are a side view and a plan view, respectively, showing an example of conventional bead inductors obtained as described above. As shown in FIGS. 14 and 15, in a conventional bead inductor, the coil 5 is embedded in a molded resin portion 8 and metallic caps 6 and 7 are attached to both end portions of the coil 5. The metallic caps 6 and 7 are electrically connected to both end portions of the coil 5 and used as external terminals.
As mentioned above, in a conventional method for manufacturing a bead inductor, after the coil defining an internal conductor is embedded in a resin material or other suitable material by injection molding, etc., it has been required that a molded body is machined or ground so as to expose both end portions of the internal conductor. It has been also required that the internal conductor and external terminals such as metallic caps are electrically connected by soldering, welding, conductive adhesives, etc. Since a break or degradation in contact is prone to occur in the electrical connection achieved by soldering, conductive adhesives, etc., there has been also a problem of a low degree of reliability of the connection.
To overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing a bead inductor to achieve increased productivity and greatly improved connection reliability between the internal conductor and the external terminals.
In accordance with a preferred embodiment of the present invention, a method for manufacturing a bead inductor includes the steps of forming an integral unitary member including an internal conductor and external terminals, the external terminals disposed at both ends of the internal conductor being electrically connected thereto; positioning the integral unitary member in a metallic mold; and molding at least one of a resin material and a rubber material including a powdered magnetic substance in the metallic mold so as to embed the internal conductor therein.
According to the one preferred embodiment of the present invention, because the integral unitary member including the internal conductor and the external terminals is used, the internal conductor and the external terminals are electrically connected in advance. Therefore, the step of exposing both end portions of the internal conductor so as to electrically connect the external terminals thereto is not required. Because the internal conductor and the external terminals are unitized in advance, connection reliability is greatly increased compared with a conventional method.
In accordance with preferred embodiments of the present invention, a through-hole for supplying at least one of the resin material and the rubber material in the periphery of the internal conductor in the metallic mold may be formed in either one or both of the external terminals. Molten resin or the like can be supplied from the outside of the external terminals in the cavity for injection molding, etc., by forming the through-hole in either one or both of the external terminals. Therefore, the metallic mold can be easily and readily designed. Dimensions and a shape of the cavity in the metallic mold can be established so as to conform to the dimensions and shape of the integral unitary member of the internal conductor and the external terminals, resulting in minimizing the amount of the resin or other suitable material being used for covering the periphery of the internal conductor and for embedding the internal conductor deposits on the external terminals.
The integral unitary member including the internal conductor and the external terminals according to preferred embodiments of the present invention may be unitarily formed by processing a metallic plate. For example, the unitary integral member including the pair of the external terminals disposed at both ends of the internal conductor can be formed by blanking a metallic plate and bending it.
The unitary integral member of the internal conductor and the external terminals according to preferred embodiments of the present invention may be formed by a simple process.
The unitary integral member including the internal conductor and the external terminals according to preferred embodiments of the present invention may be formed by unitizing separately formed internal conductor and external terminals. Therefore, the integral unitary member in which either the internal conductor or the external terminals which may have been previously difficult to form by working a metallic plate can be easily formed in preferred embodiments of the present invention. For example, the unitary integral member having a coil-shaped internal conductor can be formed according to preferred embodiments of the present invention. As for the process of forming the unitary integral member including the internal conductor and the external terminals, welding, soldering, adhesion by conductive adhesives, and other suitable methods may be used.
The internal conductor and the external terminals according to preferred embodiments of the present invention may be unitized via welding.
The strength and reliability of connection of the internal conductor to the external terminals is greatly increased via the welding.
The internal conductor according to preferred embodiments of the present invention may be coil-shaped. The length of the internal conductor can be elongated by using the coil-shaped internal conductor so that an inductance thereof is readily and easily adjustable.
In accordance with another preferred embodiment of the present invention, a bead inductor includes an internal conductor, a molded member having at least one of a resin material and a rubber material including a powdered magnetic substance with the internal conductor embedded therein, and external terminals disposed at both ends of the internal conductor and being electrically connected thereto, wherein the internal conductor and the external terminals define a pre-formed integral, unitary member.
In a bead inductor according to this other preferred embodiment of the present invention, since the internal conductor and the external terminals are arranged to define a pre-formed integral, unitary member, the manufacturing process thereof is substantially simplified and efficiency of production thereof is greatly increased. Since the internal conductor and the external terminals are arranged to be pre-formed to define an integral, unitary member in advance, connection reliability is also increased as compared with a conventional device.
The internal conductor and the external terminals according to the another preferred embodiment of the present invention may be unitarily joined to define an integral member by processing a metallic plate.
In this case, since the internal conductor and the external terminals are simultaneously unitarily formed by processing a metallic plate, the manufacturing process thereof is greatly simplified and efficiency of production thereof is significantly increased.
The internal conductor and the external terminals according to the another preferred embodiment of the present invention may be unitarily formed to define the integral, unitary member, via welding the internal conductor and the external terminals which are separately formed in advance.
In this case, since the internal conductor and the external terminals are unitized via welding, the strength and reliability of the connection between the internal conductor and the external terminals is greatly increased, resulting in a significantly increased connection reliability.
The internal conductor according to the another preferred embodiment of the present invention may be coil-shaped. The length of the internal conductor can be elongated by using the coil-shaped internal conductor so that an inductance thereof is readily and easily adjustable.
Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention which refers to the accompanying drawings.